Ring seals are often used to maintain a pressure differential between relatively rotatable sections of a turbine engine. For example, it is desirable to separate high pressure compressed air from adjacent bearing cavities, etc. A typical arrangement comprises a compressor section or shaft that is journaled for rotation relative to a fixed housing. A ring seal is accommodated in a groove in the rotatable section. The ring seal is secured against rotation but free to move axially. During normal operation, the ring seal is driven toward the low pressure section by the pressure differential between the sections. Movement of the ring seal toward the low pressure section is balanced by friction between the outer stationary member and the ring seal which effectively reduces axial reaction forces on the shaft to a value which approaches zero. This is desirable for satisfactory operation, but is a condition that exists only when the shaft is shifting toward the low pressure section. Stated in another manner, the ring seal tends to shift with the shaft toward the low pressure section due to a combination of the pressure differential across the seal and engagement thereof by the high pressure side of the shaft groove which balances out the axial reaction force of the fixed section against movement of the seal. Thus, minimum force must be exerted by the rotating section against the ring seal.
On the other hand, when the shaft or rotating section shifts toward the high pressure side of the ring seal, the low pressure side of the shaft groove must exert sufficient force to overcome both the pressure differential across the ring seal and friction between the ring seal and the stationary section. If this force is excessive, unacceptable heat is generated and wear will occur. For this reason, ring seals for high speed shafts and dry running shafts are limited to relatively low pressure drops across the ring seal.